Method for the acquisition of moving objecs through nuclear magnetic resonance tomography

ABSTRACT

A nuclear magnetic resonance (NMR) tomography method for investigating a target object, wherein radio frequency (RF) pulses are irradiated into a target volume and/or RF pulses from the target volume are detected, wherein the target volume is determined by the frequency of the RF pulses and/or through magnetic field gradients, and wherein the target object is moved relative to the NMR tomograph during NMR data acquisition, is characterized in that the frequency of the RF pulses and/or the magnetic field gradients is/are changed during NMR data acquisition such that the target volume covered by the RF pulses is moved relative to the NMR tomograph at the same speed and direction of motion as the target object during NMR data acquisition. This provides a method for investigating a target object which moves relative to the NMR tomograph during NMR data acquisition, which can be carried out in a fast and simple manner.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method of nuclear magnetic resonance(NMR) tomography for investigating a target object, wherein radiofrequency (RF) pulses are irradiated into a target volume and/or RFpulses from the target volume are detected, wherein the target volume isdetermined by the frequency of the RF pulses and/or through magneticfield gradients, and wherein the target object is moved relative to theNMR tomograph during NMR data acquisition.

[0002] NMR tomography methods with moving target objects are known fromKruger et al., Magnet. Reson. Med. 47 (2002), 224, and also fromScheffler, Proc. 9^(th) Meeting ISMRM, Glasgow (2001), 1774.

[0003] NMR tomography is mainly used for medical diagnostics to obtaininformation about the volume (i.e. the inside) of a target object, inparticular about diseased or possibly diseased regions of a human bodythereby utilizing the interaction between nuclei and electromagneticpulses.

[0004] NMR images are typically acquired in individual flat slices. Toinvestigate larger target objects, individual recordings of severalslices of the target object can be produced. When one slice iscompletely recorded, the target object is displaced slightlyperpendicularly to the slice plane relative to the NMR tomograph and afurther slice is subsequently recorded. In these simple cases, thetarget object is immobile during the actual NMR data acquisition.

[0005] Recording methods of objects which are moved during the NMR dataacquisition (mainly for use for so-called total body imaging) are knownfrom literature (see e.g. Kruger et al, Magnet. Reson. Med. 47 (2002),224) which use different principles.

[0006] Methods were developed wherein the motion occurs within therecording plane (i.e. the slice). With stationary magnetic fieldgradients, such motions produce primarily displacement of the recordingdata relative to the recorded target object. When recording methods areused which are based on repeated recording of in each case differentlylocally encoded signals, this displacement differs in correspondencewith the continuous motion of the object from one recording step to thenext. This displacement can be compensated for through correspondingdata post-processing when the displacement speed is known.

[0007] Methods for recording images during motion perpendicular to therecording plane are also known (see e.g Scheffler, Proc. 9^(th) MeetingISMRM, Glasgow, (2001), page 1774). In the conventional methods, thedisplacement speed is thereby selected such that the inconsistency ofthe data due to the displacement remains small thereby hardlyinfluencing the recording quality. In general, these methods are carriedout such that the motion advance over an image acquisition is smallcompared to the thickness of the selected volume (i.e. the volume to beinvestigated). Fast acquisition techniques such as e.g. trueFISP orgradient echo sequences are used for such recording methods, which arelargely stable compared to image artefacts caused by motion. Thesemethods still have the disadvantage that the small motion advanceprolongs the overall duration of the NMR investigation.

[0008] In contrast thereto, it is the underlying purpose of the presentinvention to present a method for investigating a target object, whichmoves relative to the NMR tomograph during NMR data acquisition, whichcan be carried out in a fast and simple fashion.

SUMMARY OF THE INVENTION

[0009] This object is achieved by a method of the above-mentioned typein that the frequency of the RF pulses and/or the magnetic fieldgradients is/are changed during the NMR data acquisition such thatduring NMR data acquisition, the target volume covered by the RF pulsesis moved relative to the NMR tomograph at the same speed and in the samedirection of motion as the target object.

[0010] The target object is moved inside of the NMR tomograph. A smallpart inside of the NMR tomograph is thereby selected as target volumefor data acquisition through the magnetic field gradients, in particularslice selection gradients and the frequency of the RF pulse. Inaccordance with the invention, the frequency of the RF pulses and/or thestrength of the magnetic field gradients is/are changed during NMR dataacquisition such that the position of this target volume is carriedalong with the moved target object thereby always obtaining the NMR datafrom the same local region of the target object.

[0011] One variant of the inventive method is particularly advantageous,wherein a slice-shaped target volume is investigated during NMR dataacquisition. Known slice selection gradients can thereby be used toselect the target volume. Carrying along of the target volume togetherwith the target object is moreover facilitated when the target objectmoves perpendicularly to the slice normal (i.e. the recording plane).The plane could also be tilted as long as the motion has at least onecomponent, other than zero, perpendicular to the recording plane.

[0012] In a particularly preferred design of this method variant, thetarget object moves parallel to the surface normal of the slice-shapedtarget volume. Target objects with long extension in one dimension canbe guided through the inside of the NMR tomograph (or also the NMRtomograph can be guided over the target object). The target object (e.g.a person) can basically be investigated along its full length, typicallywith several NMR data acquisitions from different slices and continuousmotion of the target object relative to the NMR tomograph during andbetween all NMR data acquisitions.

[0013] In a preferred variant of the inventive method, the magneticfield gradients are kept constant during the NMR data acquisition andonly the frequency of the RF pulses is changed. Permanent change of themagnetic field gradient with great precision is difficult, in particularsince the shieldings must be adjusted to the varying gradient. Incontrast thereto, exact adjustment of the frequency of the RF pulses isrelatively simple and high recording quality of the NMR data acquisitioncan be obtained.

[0014] One particularly preferred design of the method variant ischaracterized in that the following applies for the Larmor frequency ωof the RF pulses:

ω(t)=γ*B ₀ +γ*GS*v*t

[0015] wherein γ is the gyromagnetic ratio, B₀ is the static magneticfield, GS is the magnetic field gradient, v is the speed of the targetobject and t is the time. The target object thereby moves at a constantspeed relative to the NMR tomograph perpendicularly to the recordingplane. This frequency setting ensures carrying along of the targetvolume with the target object in a simple manner. Adjustment of lineartemporal changes of the Larmor frequency of the radio frequency (RF)pulses is easy.

[0016] In an advantageous method variant, the target object is uniformlymoved relative to the NMR tomograph thereby greatly facilitatingadjustment of the frequency of the RF pulses and/or the magnetic fieldgradients. Uniform motion of the target object can be easily set also ina fashion protecting the possibly human target object. A uniform motionmeans a steady, straight motion.

[0017] One method variant is also preferred, which is characterized inthat the motion of the magnetic field gradients is compensated for inthe direction of motion of the target object relative to the speed ofthe target object, in particular in that the motion of the magneticfield gradients is bipolarly compensated for such that speed-dependentdephasing of the RF pulses is eliminated.

[0018] In a further preferred method variant, a multi-echo sequence isused in accordance with the RARE method principle, wherein the pulsephase is additionally adjusted in correspondence with the CPMGconditions of the motion of the target object. The RARE method utilizesseveral excitation pulses which precludes use of this method for movingtarget objects without carrying along the target volume as in accordancewith the invention.

[0019] One method variant is also preferred, wherein a multi-slicetechnology is used for investigating ns slices. The multi-slicetechnology permits considerable reduction of the measuring time forlarger target objects.

[0020] One method of NMR tomography for investigating a target object isalso within the scope of the present invention, which is characterizedin that several NMR data acquisitions are cyclically repeated by theabove-mentioned inventive method. This permits continuous investigationof target objects of any length in the direction of motion. Each NMRdata acquisition permits investigation of another region of the targetobject which is disposed in the measuring period in the inside of theNMR tomograph in each case.

[0021] The present invention also includes a method of NMR tomographyfor investigating a target volume which is characterized in that severalNMR data acquisitions are carried out successively by theabove-mentioned inventive methods, and wherein after each NMR dataacquisition, the position of the target volume relative to the NMRtomograph is reset to an initial position. The NMR tomograph has anadmissible displacement region for the region of the target object to bemeasured in which the NMR data is recorded. After termination of the NMRdata acquisition of this region (typically this slice) the target volumereturns to investigate a new region of the target object. The targetobject can then be effectively scanned region by region.

[0022] One variant of these two last-mentioned methods is particularlypreferred, wherein a slice-shaped target volume is investigated duringNMR data acquisition, and the target object moves further by exactly oneslice thickness during one NMR data acquisition. In this case, thesuccessively investigated regions of the target object border directly,such that the target object can be completely investigated (i.e. imaged)during the entire NMR method.

[0023] One method variant is furthermore preferred, which ischaracterized in that the position of the target volume is changed by adistance ds during NMR data acquisition with m individual steps requiredfor complete slice reconstruction after k=np*m/ns individual steps,which distance ds corresponds to the spatial separation of the positionof neighboring slices, such that after acquisition of N*m individualsteps for a total of N*ns−(ns/np−1) slices, complete data is obtainedfor image reconstruction, wherein np≧1 (and preferably np=1), N≧1. Thissaves time by a factor of ns compared to the above-mentioned acquisitionwith the individual slice method for investigating large target objects.

[0024] One variant of the inventive method is particularly preferred,wherein during NMR data acquisition, two or more measuring sequences areapplied in a nested manner, wherein the measuring sequences generallyproduce signals with different contrast, and wherein each measuringsequence acts on a different partial volume of the target object. Thustwo or more image contrasts can be acquired with one single passage ofthe target object through the NMR tomograph.

[0025] Further advantages of the invention can be extracted from thedescription and the drawing. The features mentioned above and below maybe used in accordance with the invention either individually orcollectively in arbitrary combination. The embodiments shown anddescribed are not to be understood as exhaustive enumeration but haveexemplary character for describing the invention.

[0026] The invention is shown in the drawing and is explained in moredetail with reference to embodiments.

[0027]FIG. 1 shows a schematic illustration of the signal loss throughmigration of the excited region of a moving target object in accordancewith prior art;

[0028]FIG. 2 shows a schematic illustration of the signal loss throughmigration of a structure S of a moving target object in accordance withprior art;

[0029]FIG. 3 shows a schematic illustration of the phase position of aspin in a moving target object in accordance with prior art;

[0030]FIG. 4 shows a schematic illustration of the inventive method withindividual steps A1 through Am;

[0031]FIG. 5 shows a schematic illustration of the inventive principleof a continuous recording of a uniformly moving target object;

[0032]FIG. 6 shows a schematic illustration of the inventive principleof a continuous recording using a multi-slice method with ns individualsteps;

[0033]FIG. 7 shows a schematic illustration of an inventive NMR dataacquisition with 2 pulse sequences for different image contrasts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] The invention relates to NMR acquisition techniques, whereindisplacement occurs not in the plane of the recorded image (inparticular slice) but wherein the target object is displacedperpendicularly to the image plane during recording.

[0035] For considering the effect of such a displacement, it must benoted that data acquisition of a magnetic resonance (MR) image isperformed sequentially and in many acquisition methods through repeatedrecording of individual steps, which differ through change of therespective phase encoding of the individual steps in case of thegenerally used Fourier transformation method.

[0036] The motion of the target object during the recording may concernthe signal intensity of each individual step, as well as the consistencyof the total number of individual steps used for image reconstruction.

[0037] In the first case, signal loss occurs always when more than onesingle, slice-selective radio frequency pulse is used to generate asignal. This is the case e.g. for spin echo methods, wherein anexcitation pulse followed by at least one excitation pulse, in the caseof the RARE (also called TSE, FSE) method also several excitationpulses, is/are used to generate a signal. If the object moves duringapplication of such a sequence, a signal loss occurs already duringrecording of each individual step, because part of the volume to beinvestigated moves out of the volume detected by the measuring sequencethereby preventing measurement of the spins contained therein (FIG. 1).

[0038] A further effect is obtained if a structure to be representedremains to a large extent in the investigated slice during recording ofan individual step, but moves out of the volume under investigationduring recording of the total number of the individual steps (i.e. thetotal duration of an NMR data acquisition of one slice). Acquisition ofthe data required for image reconstruction is incomplete for spins fromsuch a structure S within the moving target object, which produces imageartefacts, in particular unsharpness (FIG. 2).

[0039] In addition to these partial volume effects, further signallosses or image artefacts occur in that the rephasing conditions for thegradients used during acquisition for local encoding are no longer metdue to the motion of the spins (FIG. 3). The spins experience dephasingduring slice selection through a radio frequency pulse in the presenceof a slice selection gradient due to their Larmor precession in therespectively local magnetic field which results from superposition ofthe position-independent basic field B0 with a position-dependentportion produced by the slice selection gradient. Spins at differentpositions in the direction of the gradient thereby experience differentdephasing which must be cancelled by corresponding compensating gradientsteps before signal readout. If the object does not move, this dephasingcan be compensated for in the simplest case through a following gradientof negative amplitude and identical surface. If the object moves duringthe acquisition, this motion produces a continuous change of themagnetic field at the location of the spin. The phase development ofsuch moving spins corresponds then to a quadratic form in correspondencewith:

=γΔΦ∫GS z(t) dt=½v _(z) t ² γGS,

[0040] wherein ΔΦ is the phase shift, γ is the gyromagnetic ratio, GS isthe slice-selection gradient, z is the relative position of the regionof the target object to be investigated in the NMR tomograph, t is thetime, v_(z) is the relative speed of the target object. This phase shiftis relevant mainly for so-called multi-echo methods (known as fast spinecho (FSE), turbo spin echo (TSE) or RARE (rapid acquisition withrelaxation enhancement)) since they disturb the coherence of refocusingover several echoes and therefore cause a drastic signal loss.

[0041] On the basis of the above-mentioned considerations, the followinginventive measures are found to reproduce the consistency of dataacquisition. The slice defined by the slice selection gradient and thefrequency-selective excitation pulse is carried along with the movingtarget object during acquisition such that the pulse sequence acts ineach case on identical volume regions of the moving target object (FIG.4). This is advantageously effected in correspondence with the principleof slice selection in that the slice selection gradient for theindividual excitation steps remains constant during application of thefrequency-selective radio frequency pulses—like for recording astationary object—while the selection frequency is changed in accordancewith the motion of the object.

[0042] In correspondence with the Larmor relationship, the followingapplies:

ω=γB=γB ₀ +γGS z=γB _(O) +γGS v _(z) t=ω ₀+Δω  [1]

[0043] wherein ω is the Larmor frequency, γ is the gyromagnetic ratioand B is the magnetic flux density at the location of the spin. Thelatter is composed of the flux density B₀ of the magnet used and thecontribution of the gradient GS at the location z. The respectivelocation of the moved spin at a time t results thereby from the speedv_(z).

[0044] A slice selection gradient GS of a strength of 20 mT/m and adisplacement speed of 1 cm/s thereby produces a frequency shift of ˜850Hz over 100 ms.

[0045] For use in a multi-echo experiment, the frequency shift mustoccur within each echo train, i.e. subsequent refocusing pulses havedifferent frequencies, wherein also the phase of the pulses must beselected in accordance with the CPMG conditions such that the phasecoherence of the spins is maintained.

[0046] In the simplest case of using a pulse sequence which inherentlyexcites signals from one single slice and which requires m recordingsteps for acquisition one complete data set for image reconstruction,the acquisition is performed such that the respectively selectedexcitation volume (target volume) is moved over these m steps betweenthe position A1 and Am in FIG. 5 in correspondence with the displacementspeed. The recording can subsequently be repeated, wherein, when thesame slice positions A1 through Am are selected in the moved targetobject, a new slice of the target object which is correspondinglyshifted parallel thereto due to its motion, is recorded. If the speed ofmotion is thereby selected such that Am is shifted relative to A1 by oneslice distance ds, through the cyclic repetition complete recording ofthe object is obtained.

[0047] If multi-slice recording technology with ns individual slices isused, the measuring principle can be modified as follows: The sliceposition is carried along for k=np*m/ns recording steps, whereinnp>=1<=ns. After acquisition of the recording steps A1 . . . Ak, theslice position in the resting coordinate system of the analyzing magnetis switched further by one slice distance ds (FIG. 6). After m recordingsteps, complete data for image reconstruction from Ns=ns−(ns/np−1)slices is obtained, this cycle is subsequently repeated N times toobtain in total complete data for image reconstruction from (N−1)ns+NS=Nns-(ns/np-1) slices. N is generally selected to be large such that theentire volume to be investigated (e.g. the entire body) is largecompared to the recording volume covered by the ns slices. The fact thatthe data from (ns−NS) slices is incomplete for image reconstruction, canthen be neglected.

[0048] Finally, it should be noted that the method can also be appliedusing three-dimensional position encoding. The recording steps A1 . . .Am thereby correspond to the individual steps for recording athree-dimensional data set; the recording volume is always carried alongwith the moved object.

[0049] A further, very essential and new type of application of themeasuring principle results from the finding that the method can bemodified such that recording of images with different contrast can becarried out simultaneously through application of the describedprinciples at spatially separate positions which is shown in FIG. 7. Thesignals are thereby acquired in the positions in the NMR tomographmarked by A1 . . . Am and B1 . . . Bm. Data acquisition with completelyindependent measuring sequences is thereby carried out within each ofthese two (or more) volumes under investigation (target volumes),therefore producing images with completely independent contrast. Afterpassing the body once, (almost) simultaneously generated data sets withdifferent contrast can be produced through continuous detection of theentire target object. To vary the contrast behavior of the signalsindependently of each other, the motion of the object must besufficiently slow to ensure that spins which enter the volume B underinvestigation have sufficiently recovered from the previous signalexcitation through the sequence acting on A with respect to thecontrast-relevant parameters. The sequences acting on the partial targetvolumes can thereby be configured absolutely independently of eachother. To obtain similar or identical volume coverages, it is in mostcases advantageous (but not absolutely necessary) that the sequencesattain similar or identical recording times for one recording cycle. Therecording can thereby be carried out either through nesting of theindividual steps (A1-B1-A2-B2 . . . ) or also—with sufficiently fastrecording techniques—through segment-wise nesting up to nesting of theentire recording of a data set (A1-A2- . . . Am-B1-B2- . . . Bm).

[0050] Recording methods for such nested recording with differentcontrast, which are typically and frequently used in practice, arecombinations of frequently used sequences such as T1-weighted recording,T2-weighted recording, STIR, FLAIR, diffusion-weighted recordings andmany more.

[0051] The speed-dependent dephasing of the signals which occurs duringthe measurement due to the change of location of the target object andtherefore of the spins to be investigated, can be eliminated usinggradients which are compensated for with respect to a constant speed.This is analogous to the known principle of flux-compensated measuringmethods (see e.g. Duerk et al, Magn. Reson. Imaging 8 (1990), 535). Anecessary and sufficient condition for this is that, in addition to theintegral under the gradient between excitation and reading, also theintegral of the square of the gradient is set to zero. This is obtainedin the most simple case through so-called bipolar motion-compensatedgradients.

[0052] Explanation of the Figures:

[0053]FIG. 1 shows the signal loss in a recording with fixed location ofa partial volume A, wherein the object O moves in the direction of thearrow. If the partial volume A detected by the excitation pulse isidentical with the partial volume B detected by the refocusing pulse,part of the originally excited spins (area C with inclined hatching) hasmoved out of the slice (i.e. the target volume) before refocusing anddoes therefore not contribute to signaling and the observed signaltherefore originates only from the partial volume D (crosshatched).

[0054]FIG. 2 shows the same for a structure S which moves out of thepartial volume A detected by the slice-selective acquisition (i.e. thetarget volume) during acquisition of all individual steps used for imagereconstruction and reaches the position S′ outside of this volume Aunder investigation at the end of image acquisition. Since thisstructure provides no signal contribution during part of dataacquisition, the data amount required for spatial encoding is incompletewhich produces image artefacts.

[0055]FIG. 3 shows the effect of the motion of the object on the phaseΦ(t) of spins which move along a gradient GS during the acquisition. Bis thereby the magnetic flux density which changes through applicationof a gradient linearly along the direction z of the gradient. RF showsthe excitation pulse of an MR sequence, GS(z) shows the schematicdiagram for the gradient used. A signal for stationary spins is producedwhen the integral over the gradient (hatched area) is zero. Thiscondition is not met for moving spins; they experience dephasing ΔΦ(v)which is proportional to the speed of motion.

[0056]FIG. 4 shows the principle of the inventive method: the positionof the respectively investigated slice (i.e. the target volume) iscarried along with the moved target object in the NMR tomograph, suchthat the positions of the individual steps A1 . . . Am differ in spacerelative to the NMR tomograph, but detect respectively identical volumesof the moved target object. For spin echo methods, wherein severalpulses are used for each individual step, the slice position ismaintained also within each echo train. The respective slice positionsare shown next to each other only for reasons of clarity. The slicecontinuation will generally be small compared to the slice thickness independence on the speed of motion.

[0057]FIG. 5 shows the principle of a continuous acquisition of a targetobject moving at a speed v_(z). During the time t0 . . . t1, theindividual steps A1 . . . Am which are required for acquisition of adata set from the target volume 1 are recorded wherein the recordingvolume is moved together with the target object. The procedure issubsequently repeated with a second neighboring volume 2 within a timet2 . . . t3. With multiple repetition, a target object of any size canbe successively and continuously investigated.

[0058]FIG. 6 shows the principle of continuous recording of a volumewith application of a multi-slice acquisition method with ns individualslices: The recording slice is carried along with the moved object overk=m/ns individual steps, and the recording slice is subsequentlydisplaced in the object by exactly one slice position ds.

[0059]FIG. 7 shows the principle of continuous acquisition of data withsequences which effect different image contrasts: in the partial volumecharacterized by A1 . . . Am, a sequence with a certain contrastbehavior is carried out in accordance with the above principles. In B1 .. . Bm, a second and different sequence is applied in a nested mannerthereto, which produces a different contrast. The object is detected intwo different contrasts with continuous acquisition through one singlepassage due to the motion of the object.

[0060] The invention presents an MRT method, wherein the object movestransversely to the direction of the selected volume during dataacquisition, and wherein the signal losses caused through motion of theobject and inconsistencies of recorded data are prevented in that thevolume to be investigated is carried along with the moving object andall general conditions required for signal generation with respect tomagnetic field gradient and the radio frequency pulses used, areadjusted to the motion of the object.

We claim:
 1. Nuclear magnetic resonance (NMR) tomography method forinvestigating a target object, wherein radio frequency (RF) pulses areirradiated into a target volume and/or RF pulses from the target volumeare detected, wherein the target volume is determined by the frequencyof the RF pulses and/or through magnetic field gradients, and whereinthe target object is moved relative to the NMR tomograph during NMR dataacquisition, characterized in that the frequency of the RF pulses and/orthe magnetic field gradients is/are changed during NMR data acquisitionsuch that the target volume covered by the RF pulses is moved at thesame speed and in the same direction of motion as the target objectrelative to the NMR tomograph during NMR data acquisition.
 2. Methodaccording to claim 1, characterized in that during NMR data acquisition,a slice-shaped target volume is investigated.
 3. Method according toclaim 2, characterized in that the target object moves parallel to thesurface normal of the slice-shaped target volume.
 4. Method according toclaim 1, characterized in that the magnetic field gradients are keptconstant during NMR data acquisition and only the frequency of the RFpulses is changed.
 5. Method according to claim 4, characterized in thatthe following applies for the Larmor frequency ω of the RF pulses:ω(t)=γ*B _(o) +γ*GS*v*t, wherein γ is the gyromagnetic ratio, B_(o) isthe static magnetic field, GS is the magnetic field gradient, v is thespeed of the target object and t is the time.
 6. Method according toclaim 1, characterized in that the target object is uniformly movedrelative to the NMR tomograph.
 7. Method according to claim 1,characterized in that the movement of the magnetic field gradients iscompensated for with respect to the speed of the target object, in thedirection of motion of the target object, in particular, that the motionof the magnetic field gradients is bipolarly compensated for.
 8. Methodaccording to claim 1, characterized in that a multi-echo sequence inaccordance with the principle of the RARE method is applied, wherein thepulse phase is additionally adjusted to the motion of the target objectin accordance with the CPMG conditions.
 9. Method according to claim 1,characterized in that a multi-slice technology is applied forinvestigating ns slices.
 10. Method of NMR tomography for investigatinga target object, characterized in that several NMR data acquisitions arecyclically repeated through methods in accordance with claim
 1. 11.Method of NMR tomography for investigating a target object,characterized in that several NMR data acquisitions are subsequentlycarried out through methods in accordance with claim 1, and whereinafter each NMR data acquisition, the position of the target volumerelative to the NMR tomograph is reset to an initial position. 12.Method according to claim 10, characterized in that during an NMR dataacquisition, a slice-shaped target volume is investigated, and thetarget object moves further by exactly one slice thickness during oneNMR data acquisition.
 13. Method according to claim 10, wherein duringNMR data acquisition, a slice-shaped target volume is investigated,characterized in that in NMR data acquisition with m individual stepsrequired for complete slice reconstruction after k=np*m/ns individualsteps, the position of the target volume is changed by one slicethickness to obtain complete data for image reconstruction afteracquisition of N*m individual steps for a total of N*ns−(ns/np−1)slices, wherein np>1, N>1.
 14. Method in accordance with claim 1,characterized in that during NMR data acquisition, two or more measuringsequences are applied in a nested manner, wherein the measuringsequences generally produce signals with different contrast, and whereineach measuring sequence acts on a different partial volume of the targetobject.